[otrs] Can't set service or SLA for a new ticket

Hi, I am not able to set Service or SLA when I create a new ticket, although I have already make the setting in "Ticket Settings"->"SLAs" and "Services". When I try to create a new ticket, the "Service" or "SLA" can't be lanced automatically. The OTRS version is 3.0.8. Thanks for any reply! Xiaoxing